In recent years, the development of a close proximity wireless transfer technology has been promoted. The close proximity wireless transfer enables communication between two devices which are brought close together. Each of the devices having close proximity wireless transfer functions includes a coupler. When the two devices are brought close together within the range of communication, the couplers of the two devices are electromagnetically coupled. By this coupling, the devices can wirelessly transmit and receive signals.
A typical coupler includes, for example, a coupling element, an electrode pole, a resonance stub, and a ground, and the like. The resonance stub functions as a resonance module. The resonance stub is formed by a conductor pattern on a printed circuit board. A signal is supplied to the coupling element via the resonance stub and the electrode pole. As a result, an electric current flows in the coupling element, and an electromagnetic field is generated around the coupler. This electromagnetic field enables electromagnetic coupling between the couplers which are provided in the two devices which are brought close together.
In the meantime, a coupler is required to have a sufficient tolerance to a positional displacement between this coupler and a counterpart coupler. This aims at preventing the wireless communication between the devices from being affected, even when the positional relationship between the devices which are brought close together is slightly varied.
In addition, the coupler which is included in the device is required to have a high impedance. The reason for this is that if the coupler is mounted in the device, coupling would occur between the coupler and other peripheral components in the device, leading to a decrease in input impedance of the coupler. The decrease in input impedance is a factor which degrades the electromagnetic field radiation efficiency of the coupler.
Moreover, recently, there has been a demand for a lower height of the coupler, so that the coupler may easily be mounted in various devices.